Which plants have compound leaves? Plant leaves

The main part of an ordinary leaf is its blade. Leaf blade- This is an expanded flat formation that performs the functions of photosynthesis, gas and water exchange. In addition to the blade, the leaves often have petiole- an elongated cylindrical stem-like part with which the plate is attached to the stem. If there is a petiole, the leaf is called petiolate, and if it is absent, it is called sessile. The bottom of the sheet is its base– can grow and envelop the stem in the form of a tube. This formation is called a leaf sheath. Quite often, at the base of the leaf at the petiole there are special outgrowths - stipules. Stipules are paired, of various shapes and sizes, green or colorless, free or fused with the petiole. The stipules may or may not fall off as the leaf grows.

Simple leaves are those that have one leaf blade on a petiole, while a complex leaf has several blades called leaflets attached to one petiole.

Simple sheet. Leaf blade simple sheet can be whole or, on the contrary, dismembered, i.e. to one degree or another, rugged, consisting of protruding parts of the plate and grooves. To determine the nature of dissection, the degree and form of ruggedness of leaf blades and the correct name of such leaves, first of all, one should take into account how the protruding parts of the blade are distributed - blades, lobes, segments - in relation to the petiole and the main vein of the leaf. If the protruding parts are symmetrical to the main vein, then such leaves are called pinnate. If the protruding parts emerge as if from one point, the leaves are called palmate. Based on the depth of the cutouts of the leaf blade, leaves are distinguished: lobed, if the notches (depth of cuts) do not reach half the width of the half-blade (the protruding parts are called blades); separate, with a depth of cutouts extending deeper than half the width of the half-plate (protruding parts - lobes); dissected, with the depth of the cuts reaching the main vein or almost touching it (protruding parts - segments).

Complex leaf. Compound leaves, by analogy with simple ones, are called pinnate and palmate with the addition of the word “complex”. For example, pinnately compound, palmate compound, ternate compound, etc. If a compound leaf ends in a single leaflet, the leaf is called imparipinnate. If it ends in a pair of leaflets, then it is called paripirnate.
The division of the blade of a simple leaf, as well as the branching of parts of a complex leaf, can be repeated. In these cases, taking into account the order of branching or division, they speak of double-, triple-, quadruple-pinnate or palmate, simple or compound leaves.

Basic forms of leaf blade

Types of division of blades of simple leaves and classification of complex leaves

Basic types of sheet edges

1 - entire; 2 - notched; 3 - wavy; 4 - spiny; 5 - toothed; 6 - double-toothed; 7 - serrated; 8 - crenate

Top shapes The shapes of the apex, base and edge of leaf blades are also features used in describing and identifying plants.

Basic shapes of the tip of the leaf blade

Shapes of the base of the leaf blade

Main types of leaves

palmate leaf shape

When all the leaves are radially attached to the top of the main petiole, this is palmate leaf shape (horse chestnut, virgin grapes, cinquefoil, lupine). Usually the descriptions mention the number of leaflets attached to the main petiole. Palmately compound leaves consisting of three leaflets are often found and are called trifoliate: clover, strawberry, stoneberry, blackberry, sweet clover, oxalis.

trifoliate leaf shape

Needles.

In conclusion, let us mention one of the ancient forms leaves: needle-shaped, or needles (Fig. 18). They are thin, narrowly linear, leathery, with a pointed tip, can be soft or quite hard, prickly, well adapted to withstand unfavorable climatic conditions (frost or heat), live on the plant for several years (with the exception of some species), in addition, When alive, they release special substances into the atmosphere - phytoncides, which affect the composition of the air microflora. This is the most typical leaf shape of coniferous plants. (fir, spruce, pine, larch, juniper, cypress, etc.)

Leaf morphology. The leaf of most plants consists of a leaf blade, a petiole, and many leaves have stipules. The leaf blade is the expanded, usually flat part of the leaf that performs the functions of photosynthesis, transpiration and gas exchange.

The shape of plastic sheets can be round, oval, elliptical, ovoid, linear, lanceolate, arrow-shaped, spear-shaped and others. The shape of the edge of the leaf blade (Fig. 23) can be: entire, serrated, serrate, crenate, notched, etc.

Rice. 23. Shape of the edge of the leaf blade

1 - whole-edged; 2. - ciliated; 3 - serrated; 4 tooth; 5 - plow-shaped; 6 - crenate; 7 - wavy; 8 - notched.

Rice. 24. Dissection of the leaf blade:

1 - pinnately lobed;

2 - pinnately separate;

3 - pinnately dissected;

4 - finger-lobed;

5 - finger-separate;

6 - finger-dissected.

The leaf blade can be whole or dissected. The dissection can be finger-like or feathery. If the dissection of the edge does not exceed one quarter of the width of the half-blade, then the leaves are called whole, but if the dissection of the blade is greater, then such leaves are called dissected.

According to the degree of dissection of the leaf blade, they are distinguished (Fig. 24) lobed leaves - notches do not reach half of the half-blade (oak), separate – the notches go deeper than half of the half-plate (geranium), dissected leaves - notches reach the main vein of the leaf (potato, crow's foot).

petiole– a narrowed part of the leaf that connects the leaf blade to the base and regulates the position of the leaf in relation to the light. Leaves with petioles are called petiolate , without petioles – sedentary . If the base of the leaf is in the form of a tube covering part of the stem (wheat), then such leaves are called vaginal .

Stipules- leaf-shaped formations at the base of the leaf, which serve to protect the young leaf and axillary bud. Not found in all plants. Most plants have no stipules on adult leaves (oak). Sometimes the stipules reach significant development, their size exceeds the size of the leaf blades (peas). In this case, the stipules act as photosynthetic organs.

A leaf usually consists of an expanded part - the leaf blade - and a more or less round, thin part - the leaf petiole, which is attached to the stem. Sometimes the leaves do not have a petiole and are connected directly by the leaf blade to the stem. Such leaves are called sessile.

If a sessile leaf has a notch at the base of the plate and its edges seem to encircle the stem, this is a stem-encompassing leaf, and its blades enveloping the stem are called ears.

In some plant species, the lower part of the leaf covers the stem in the form of a tube - a vagina. Such leaves are called vaginal.

Small and sometimes quite large leaves at the base of the leaf are called stipules.

According to the shape of the leaf blade, the leaves can be linear, lanceolate, elliptical, ovate, cordate, obverse-cordate, kidney-shaped, thyroid, round, spatulate, sagittal, spear-shaped, needle-shaped and filiform.

Leaf blades sometimes do not have any cutouts along the edges, like entire leaves.

If they are cut no more than a quarter of the width to the main vein, these are useful leaves. The teeth along the edge of serrated leaves look like more or less equilateral triangles, but in serrated leaves they are not equilateral and their apex is directed towards the top of the leaf. There are teeth and rounded shapes - in crenate leaves.

If the notches between the teeth are more or less rounded, the leaf is called notched.

Leaves can be lobed, divided or dissected. In a lyre-shaped, pinnately dissected leaf, the apical lobe has a rounded shape and is much larger than the other lobes; in a pluriform leaf, it resembles a triangle.

The veins on the leaves are clearly visible. Sometimes they are arranged in parallel rows (in the leaves of the parallel nerves), sometimes they bend in an arc (in the arcuate nerves), or extend pinnately from the main vein (in the pinnate nerves), or fan out from it (in the palmate nerves).

The angle between the petiole and the stem node to which the leaf is attached is usually called the axil.

If a leaf has one leaf blade, it is a simple leaf. But the leaves of many plants consist not of one, but of several leaf blades and therefore are called complex. Their plates are clearly separated from each other, but with their petioles they are attached to one common petiole.

Compound leaves can be of three types: trifoliate, with three palmately arranged leaflets; palmate or palmate, when the leaflets extend from one place at the end of a common petiole, and pinnate (pairwise arrangement of leaflets on a common petiole). If a pinnate leaf has a terminal unpaired leaflet, the leaves are called odd-pinnate, and if it is absent, they are called pair-pinnate. Often, on a common petiole, pairs of larger leaves alternate with pairs of smaller ones - these are intermittently pinnate leaves.

If the leaflets of a pinnate leaf sit in pairs not on the main petiole, but on its second-order branches, the leaves are called bipinnate; when located on the third-order branches of the petiole, they are called trippinnate.

The leaves are connected to the stem node often one at a time and rise along the stem from bottom to top, as if in a spiral, forming a spiral leaf arrangement. There is also an opposite leaf arrangement, when two leaves are attached to each stem node (one opposite the other), and a whorled leaf arrangement, when several leaves are connected to one stem node.

Autumn is one of the most beautiful times of the year. The diversity and richness of nature during this period simply amazes the mind, the simple and complex leaves are so different from each other. The leaf arrangement of each plant is special (it can be alternate or whorled), and it is by this that one can determine which species it belongs to. Let's take a closer look at the features and functions of each type of leaf.

Definition in botany

Along with flowers, roots, stems and shoots, leaves are the most important vegetative organs in plants, which are also responsible for the function of photosynthesis. In addition, they perform many other jobs, such as participating in the processes of respiration, evaporation and guttation of plants. There are the following simple and complex ones, each of them has its own characteristics and is found in a certain type of plant.

Very often, leaf blades are mistaken for leaves, but in fact it is an organ that consists of a blade (veins run through it) and a stalk, which originates at the base and connects the leaf blade with stipules. It always occupies a lateral position on the stem, with all the leaves arranged on it in a certain sequence in such a way as to ensure optimal access to the sun's rays. Its dimensions can vary from 2 cm to 20 m (for tropical palm trees).

External structure and forms

One of the features of these organs is their flat shape, which ensures maximum contact of the plant surface with the air and sun rays. The shapes are simple and differ from each other in appearance. Simple ones have only one leaf blade, which is connected to the base using a petiole. Complex ones consist of several leaf blades located on one petiole. Remember what the thickest vein looks like in the middle, to which two or three stipules are attached on each side. Such a complex one is called opposite, because the leaf blades are located symmetrically to each other.

The main components are the plates and veins that run along their surface, as well as the petiole, stipules (although not all plants have them) and the base with which the element is connected to the stem of a tree or other plant.

Unlike the shape of a simple leaf, several varieties can be found in complex ones, which have their own distinctive properties and features.

Internal structure

The upper surface of the leaf blades is always covered with skin, which consists of a layer of colorless cells of the integumentary tissue - the epidermis. The main functions of the skin are protection from external mechanical damage and heat exchange. Due to the fact that its cells are transparent, sunlight passes through it unhindered.

The lower surface also consists of these transparent cells, tightly adjacent to each other. However, among them there are small paired green cells, between which there is a gap. This part is called the stomata. By opening and reconnecting, green cells open and close the entrance to the stomata. During these movements, moisture evaporation and gas exchange occur. It is known that on the surface of one leaf blade there are from 90 to 300 stomata per 1 mm 2.

Interesting fact: Green cells are almost always located on the side of the leaf where maximum air exchange occurs. So, for example, in plants floating on water, egg capsules or water lilies, the stomata are on the outer side facing the air.

Varieties

Scientists distinguish two main types of leaves: a simple leaf and a complex leaf. The structure of each of them has its own characteristics. Depending on the appearance, the number of plates and the shape of their edges, compound leaves can also be divided into several types. So, here are the most common types, if selected by external characteristics:

• fan-shaped (shape resembles a semicircle);
• spear-shaped (sharp, sometimes there are spines on the surface);
• lanceolate (rather wide, with narrowed edges);
• oval (ovoid shape, which sharpens slightly closer to the base);
• palmate and lobed (they can sometimes be confused, since they both have several lobes);
• palmate (plates diverge from the petiole, appearance resembles fingers);
• needle-shaped (thin and quite sharp).

This list can be continued for a long time, but the complex shape of the leaf has several more types, depending on the shape of the edges, as well as the location of the leaf blades themselves.

Types of complex plants

By the edges of the plates you can often determine which species a particular plant belongs to. The following forms are most common in nature:

• whole-edged - have smooth edges with no teeth at all;
• serrated - as the name implies, such leaves have teeth along the edges;
• fine-toothed - they resemble a saw, which has very sharp and small incisors;
• wavy - these have wavy cuts that do not have a strict order or standard shape.

Features of each type

It is worth talking in more detail about the distinguishing features of simple and compound leaves, as this can help determine what kind of plant it is and what species it belongs to. So, one of the most noticeable features of each type is the number of plates. If three elements are present, then we have trifoliate sheets. If five are palmate, and if there are more, then they are called pinnately divided. On each plate one can observe a special venation system, thanks to which the internal tissues receive nutrients. In simple and complex varieties they differ in shape and structure. Here are the most common types of vein arrangement:

• arcuate (when the veining resembles the shape of a menorah - one of the symbols of Judaism);
• transverse;
• longitudinal;
• palmate;
• parallel;
• mesh;
• feathery.

Another distinguishing feature is the way the leaves are arranged on the stem. Simple and complex - all, without exception, are attached to plant stems in two ways:

• using a cutting, in which case the plant is classified as petiolate;
• without a cutting, when the base grows and covers the stem, then we have a sessile plant.

Plant leaves: simple and complex

If we classify plants according to leaf characteristics, we can note the following facts. Simple ones are usually common in everyone herbaceous plants, including shrubs and trees. Complex ones are found in both shrubs and trees, however, unlike simple ones, during leaf fall they do not fall off all at once, but in parts: first the blades themselves, and then the cuttings.

Let's look at the names of simple and complex leaves in plants using examples. Most trees growing in Russia have simple leaves. Aspen, birch and poplar have different shapes: lanceolate, rounded with jagged edges and spear-shaped, respectively. With the onset of autumn cold, the leaves of each of them fall off completely. They are also found in fruit trees such as apple, pear and cherry; crops such as oats and corn also have simple leaves.

Complex forms are present on leguminous plants, such as the pinnately compound leaves of peas. The palmate leaves have next trees: maple, chestnut, lupine, etc. Remember red clover, its shape is called trifoliate with ciliated edges.

What functions do leaves perform?

The simple and complex forms of these organs are largely due to climatic conditions. In hot countries, trees have large leaves, which serve as a kind of protective fence from the sun's rays.

However, the main irreplaceable function is participation in photosynthesis. As you know, it is through this process that trees can convert carbon dioxide into oxygen by absorbing solar energy.

The second most important process is cellular respiration. With the help of mitochondria, leaves take in oxygen, and through the stomata they exhale carbon dioxide, which is then used during photosynthesis. Since photosynthesis occurs only in light, carbon dioxide is stored at night in the form of organic acids.

Transpiration is the evaporation of water from the surface of leaves. Thanks to this, the overall temperature and humidity of the plant is regulated. The intensity of evaporation depends on the size and thickness of the plates and on the wind speed at a certain point in time.

Adaptation and modification

Many leaves - simple and complex - have the ability to adapt to conditions environment. In the process of evolution, they acquired the ability to change. Here are the most amazing of them:

• the ability to produce wax that lies on the surface and prevents excessive evaporation of water droplets;
• they form reservoirs for water during rains, this happens due to the fusion of the edges in such a way that a bag-like container is formed (such forms can be found in many tropical vines);
• the ability to change the surface of the plates, rugged leaves prevent the effects of strong winds, thereby protecting plants from damage.

Many facts related to the life activity of these irreplaceable plant organs still remain poorly understood. These beautiful decorations of nature itself, in addition to the above functions, perform another aesthetic task - they delight people with their splendor and variety of bright colors!